1. Field of the Invention
The invention relates to techniques of preliminary firing of ink droplets through inkjet nozzles prior to ink ejection for an image recording cycle.
2. Description of the Related Art
There are known as recoding devices for forming desired image(s) on a recording medium, such as a sheet of paper, inkjet recording devices configured to form desired image(s) on the recording medium using a printhead having thereon an array of plurality of inkjet nozzles and orifices in which the inkjet nozzles terminate. The inkjet recording devices are of, for example, piezoelectric-type, thermal-type (or bubble-jet-type), or the like.
During the use of such inkjet recording devices, air bubbles, dust or dirt could be introduced into ink collected within inkjet nozzles terminating in inkjet orifices, and the collection of ink could rise in viscosity due to evaporation of the ink solvent.
For those reasons, it is conventional to perform preliminary firing or expelling of ink droplets through the inkjet nozzles prior to firing of ink droplets for an image recording cycle, for removal of performance-degrading factors, such as air bubbles, dust or dirt, from the inkjet nozzles. This preliminary firing, in general, is repeated during a succession of operation of inkjet recording devices.
An example of a conventional version of such inkjet recording devices is disclosed in Japanese Patent Application Publication No. HEI 5-338134.
In this example, a gross quantity of ink droplets ejected or equivalently the total number of ink droplets ejected (hereinafter, referred to as “expelled-drop count”) is measured on a per-inkjet-nozzle basis. Further, time intervals at which successive cycles of preliminary firing of ink droplets are controlled as a function of the measured gross-quantity of ink droplets ejected or expelled-drop count, eventually resulting in a controlled total-number or frequency of cycles of preliminary firing performed.
More specifically, in this example, when a scheduled timing of preliminary firing of ink droplets is reached, and when, at the same time, the smallest one of the expelled-drop counts which have been measured for the inkjet nozzles, respectively, is large enough to make it unnecessary to perform preliminary firing of ink droplets as scheduled, the time intervals between cycles of preliminary firing are prolonged, without performing preliminary firing as scheduled, despite that the scheduled timing of preliminary firing has been reached.
It would be desirable to reduce an amount of ink to be spent by preliminary firing only for cleaning the inkjet nozzles.